Conventionally, many molded articles of styrene-based resins, such as ABS resin, have excellent electrical insulation. In electrostatically coating the molded article, the surface of the molded article to be coated should be conductive. As a method for making the resin surface conductive, a method for coating the resin surface with a conductive primer or a method for kneading the resin and a metal filler, such as a conductive carbon, is usually used. However, with the method for coating the resin surface with a conductive primer, variations in the film thickness of the conductive primer deteriorates the electrostatic coating property (the coating efficiency). In addition, the primer coating step makes the process complicated. Furthermore, with the method for kneading the resin and a conductive filler, if the filler is poorly dispersed, a coating unevenness occurs and the impact strength of the resin decreases.
In general, in order to electrostatically coat the resin molded article with good efficiency, the article to be coated should be a conductive material (a surface resistivity of 10.sup.10 .OMEGA. or less). Conventionally, as a method for decreasing the surface resistivity of the resin, for example, 1 a method for kneading the resin and a surfactant having a low molecular weight or coating the resin with the surfactant, and 2 a method for kneading a polyamide-based elastomer having a high molecular weight generally called a permanently antistatic agent (Japanese Patent Application (Tokko Hei) No. 4-72855) are disclosed.
However, with the above method 1, the desired conductivity cannot be provided in many cases because the antistatic agent is washed off when a washing treatment is performed in a degreasing step before coating. In addition, even if coating can be performed, the antistatic agent bleeds onto the surface of a coating film after coating, causing blisters (surface roughness). Therefore, this method is substantially difficult to use. With the method 2, the bleeding problems as in 1 is eliminated because a material having a high molecular weight is used. However, since a generally used polyamide-based elastomer comprises polyoxyalkylene glycol whose constituent unit is an oxyethylene group for providing conductivity, the water resistance is poor, deteriorating the water resistance and adhesion of the coating film significantly.